Biotransformation of the isoflavonoids biochanin A, formononetin, and glycitein by Eubacterium limosum

Eubacterium limosum (ATCC 8486), a strict anaerobe from the human intestinal tract that is capable of O-demethylation of several compounds, was tested for the ability to metabolize three methoxylated isoflavonoids, biochanin A, formononetin, and glycitein. High-performance liquid chromatography elution profiles of metabolites produced from biochanin A, formononetin, and glycitein showed peaks that had identical retention times to authentic genistein, daidzein, and 6,7,4′-trihydroxyisoflavone, respectively. The metabolites were identified, using an on line liquid chromatography-electrospray mass spectrometer. E. limosum produced 61.4 μM of genistein and 13.2 μM of daidzein from 100 μM of biochanin A and formononetin, after 26 days incubation. O-demethylase activity is cell-associated and was not detected in the extracellular fraction of bacterial culture. This is the first study in which conversion of biochanin A, and formononetin to more potent phytoestrogens by a bacterium has been shown.